In both open and endoscopic surgeries, it often is necessary to seal or weld blood vessels, both veins and arteries, ranging in size from less than 1 mm in diameter to more than 6 mm in diameter. For example, in subfacial endoscopic perforator surgery or SEPS, a series of perforator vessels in a patient's leg are sealed closed to alleviate venous ulcerations. In a typical SEPS procedure, the surgeon uses a mechanically deformable clip to pinch off such perforator vessels. A single clip may not seal a vessel in a reliable manner and the surgeon typically uses multiple clips on each perforator vessel to assure an effective seal. It would be preferable to seal a vessel without leaving a metal clip implanted in the patient's body.
Radiofrequency ("RF") instruments for sealing blood vessels have been developed. An example of a previously known bi-polar grasper, shown in FIG. 1A, typically applies from 40 watts to 100 watts or more of power to the exterior of a vessel to cauterize such vessels or vascularized tissue masses. To use such previously known bi-polar instruments, a blood vessel is squeezed between the opposing jaw faces of the grasper (see FIG. 1B). Each jaw face carries a conductive electrode 2A, 2B. When operating in a bi-polar fashion, an RF current generally flows directly between electrodes 2A and 2B, and "across" vessel 3, as indicated by the arrow in FIG. 1B.
Additionally, there may be stray RF current flow in circuitous low resistance routes, e.g., outwardly along the vessel and then through surrounding tissue, to reach the other electrode. This type of stray RF current flow is undesirable. For example, in a SEPS procedure or when sealing a branch vein of any arterial conduit that may be mobilized for a bypass, it is undesirable to have stray RF current affect the arterial conduit.
In using a previously known device such as depicted in FIGS. 1A-1B, the impedance of the tissue of the vessel wall changes continuously during the application of RF, making sealing erratic. The high levels of power typically used in previously known devices (e.g., 40 to 100 watts), makes the tissue impedance levels undesirably change very rapidly. At power levels ranging from 40 to 100 watts, impedance levels typically will increase within a few seconds to a level such that RF energy flow is impeded or restricted altogether, and may contribute to an increase in stray RF current. Moreover, the vessel walls often will not be fused together over a sufficient area to provide an effective seal.
Furthermore, previously known devices, such as shown in FIGS. 1A-1B, which simply clamp the vessel walls together, often entrap blood between the luminal surfaces. This trapped blood acts as a heat sink and may adversely affect the uniformity of RF thermal effects. It has been observed that the entrapment of blood within the lumen significantly interferes with the binding characteristics of the denatured proteins that are created and that comprise the amalgam for fusing the vessel walls together.
It would therefor be desirable to provide an RF energy delivery system, and methods of use, that control the effects of variable tissue impedance, thereby allowing an effective energy delivery profile in the tissue targeted for welding.
It also would be desirable to provide an RF energy delivery system, and methods of use, wherein an openable/closeable working end reduces the risk of entrapping blood between the vessel walls.
It further would be desirable to provide an RF energy delivery system, and methods of use, that reduce tissue charring and smoke, which can obscure the physician's view, particularly in endoscopic surgeries.
It still further would be desirable to provide an RF energy delivery system, and methods of use, that reduce the outward spread of thermal effects along a vessel.